Oil circuit breaker including contact braking device

ABSTRACT

An oil circuit breaker includes stationary contacts and a movable contact disposed in an arc-quenching chamber. When the movable contact is separated from the stationary contacts, a braking device coupled to the movable contacts limits the rate of travel thereof through the quenching chamber so that the movable contact remains in an area most suitable for current interruption by oil flow during at least one zero crossing of the current therethrough. The braking device comprises an oil-filled housing including a stationary, inner cylinder, a piston slidable in the inner cylinder which is coupled to the movable contacts, and a spring-loaded, outer cylinder surrounding the inner cylinder. Various apertures are provided in the cylinders and in the piston to furnish a braking action which increases with increases in the rate of initial movement of the movable contact. In any case, once the movable contact has moved out of the area of most suitable current interruption, the braking force exerted on the movable contact is decreased.

United States Patent Inventors TakumiMitsuhashi;

Kenichiro Sasaki, both of Kyoto, Japan Appl. No. 888,750 Filed Dec. 29, 1969 Patented Oct. 5, 1971 Assignee lnoue Electric Mfg. Co., Ltd.

Kyoto, Japan Priority Dec. 30, 1968 Japan 44/482 OIL CIRCUIT BREAKER INCLUDING CCNTACT BRAKING DEVICE 1 Claim, 5 Drawing Figs.

US. Cl. 200/150 B, 200/34 Int. Cl. 11011: 33/68 Field of Search 200/150 B,

References Cited UNITED STATES PATENTS 1,696,604 12/1928 Hilliard 200/ 150 B 1,768,949 7/1930 Denison 335/62 2,156,388 5/1939 Grosse 200/150 B 2,804,513 8/1957 Oppel 200/34 3,118,996 1/1964 Forwald 2001148 B FOREIGN PATENTS,

1,233,458 2/1967 Germany ZOO/148 Primary Examiner-Robert S. Macon AttorneyChristensen & Sanbom which is coupled to the movable contacts, and a springloaded, outer cylinder surrounding the inner cylinder. Various apertures are provided in the cylinders and in the piston to furnish a braking action which increases with increases in the rate of initial movement of the movable contact. In any case, once the movable contact has moved out of the area of most suitable current interruption, the braking force exerted on the movable contact is decreased.

OIL CIRCUIT BREAKER INCLUDING CONTACT BRAKING DEVICE parted from the stationary contacts but before the moving contact goes out of a quenching chamber. Generally, the quenching chamber is composed so that when the moving contact has separated from the stationary contacts and comes to a most suitable position in the chamber for extinguishing the arc that has arisen between both contacts, interruption of a specified current may be carried out. The position is decided with concern for the frequency of the interrupting current and the parting speed of the moving contact. Interruption is achieved by recovery of the insulation among the stationary and moving contacts at the time of current-zero after opening of the contacts. Recovery'of the insulation may be attained when a proper parted distance exists between the contacts and the area around the leaving end of the moving contact has been disturbed by oil-flow. For the parting distance of the poles, proper spaces capable of withstanding the transient recovery voltage between the poles are needed. The parting distance is related to the parting speed of the moving contact. The speed of the moving contact depends on not only the actuating force externally given by the tripping motion but also the self-made gas pressure in the chamber caused by the arcing heat. With increase of gas pressure, the parting speed of the moving contact increases too. Arcing heat is higher when the current becomes larger so that the gas pressure is also higher. For oil-flow to disturb the area about the moving contact end it is necessary to prepare a flowing oil path. As to the oil-flow (blast), generally there are two means to form the oilpath. One is axial-flow by use of pressure difierentials gradually becoming smaller toward lower parts of the chamber and the other is crossflow, transverse to the arc length, through openings provided in the sidewall of the chamber. The velocity of oil-flow is naturally increased with increase of pressure owing to the above-mentioned arcing heat. However too high a pressure requires high mechanical strength of the chamber. Arc pressure becomes higher with extension of the arc length. Therefore, it is required to finish the interruption while the arc length does not become too long.

Thus, if zero-current is encountered when the parted distance between the contacts is sufficient for recovery of insulation and the area about the contact end has been surely disturbed by oil-flow, very reliable interruption will be expected And it is desirable that interruption is fulfilled at initial zero'current after opening of the contacts. This is because if interruption at initial zero-current fails, the distance between the separated contacts will be so extended by the further proceeding of the moving contact that at the next zero-current, the moving contact will have passed over the most suitable position or in the worst case may have gone out of the chamber. Extension of the parted distance increases the pressure and also the speed of the moving contact, thus, it will help again the extension of the distance by itself, and it may be a cause to break the quenching by the gas pressure. In failure of interruption at initial zero-current, by use of a longer and stronger chamber, interruption at the next or the followed zero-current may be possible, but it will be 'uneconomical for use of large-siud chambers and/or large-sized breakers.

The principal object of this invention is to provide a small quenching chamber having reliable interrupting charactcristics. Another object of this invention is to give a braking (restraining) action to the moving contact departing from the stationary contacts. This braking action works only in the neighborhood of the most suitable position for quenching in the chamber. By this action, velocity of the moving contact, in the neighborhood of the most suitable position for quenching in the chamber, decreases. In other words, the time required for the contact to pass the prescribed neighborhood in the chamber becomes longer. This means that there will be more in the chamber is made long, it is desirable to bring quickly the moving contact to the above-mentioned neighborhood, in order to increase the chance of encountering zero-current. In this manner, it will be possible to increase the number of times to encounter the first or following zero-current. To increase the initial parting velocity of the moving contact is another object intended for this invention.

After the moving contact passed over the most suitable position for quenching, the motion is released from the braking action and makes the moving contact go out of the chamber swiftly. But just before the end of motion, decreasing of the speed is required for the following reason: The mechanism to stop the motion of the moving contact will receive violent shock, where continued high speed, however it is known that a shock absorber is available in such case. The methods used hitherto to decrease the speed of the moving contacts are not for the purposes to increase the chance of encountering the zero-current at the most suitable position for interrupting in the chamber, but for the purposes as buffer or damping devices.

The invention will be better understood from the following description of a preferred embodiment thereof with reference to the accompanying drawings, wherein:

FIG. I is a vertical section of the braking device of the oil circuit breaker of the invention;

FIG. 2 is a perspective view of the external cylinder used in the braking device of FIG. 1;

FIG. 3 is a view similar to FIG. 1 but showing the internal cylinder;

FIG. 4 is a vertical section of the quenching chamber of the circuit breaker; and

FIG. 5 is a graph showing the braking characteristics of the device shown in FIG. 1.

Now referring to the drawing, first to FIG. 1, the braking device of the invention is designated by 10. A cylindrical case 11 is enclosed by a base 12 which has a projecting part 13. Upper part of case 11 forms a flange 14. By means of flange 14 cover 15 is fixed to case 11. The cover 15 has a projecting part 16 corresponding to base projection 13. An internal cylinder 17 is fitted to the respective projections 13 and 16 at both ends. The cylinder 17 has a couple of slots 18 and 19 on the upper end, as shown in FIG. 3, and is provided with two holes 20 and 21 for oil path. Around the wall of internal cylinder 17, an external cylinder 22 is slidably fitted. Lower end of the external cylinder has a fiange 23 which supports a coil spring 24 against the cover 15. The spring 24 biases the external cylinder downward. At its open upper end, the cylinder 22 has a U-shaped bridge 25 with a center hole 27 through which a piston rod 33 passes. In the sidewall of the cylinder 22, two holes 30 and 31 for oil flow are formed. They are spaced apart the same distance as the two holes 20 and 21 of the internal cylinder. The rod 33 has a piston 32 and projects through the bridge hole 27 and cover 15 upwardly. Within the cylinder case 11 and in the inner space of internal cylinder 17, damping oil is contained.

FIG. 4 shows the quenching chamber 40. The chamber is composed of quenching plates 42 of pile assembly inside the cylindrical wall 41. The quenching plates are so assembled as to provide openings 45, to 45, for oil-jet along the moving contact route from the bottom end of the stationary contacts. Lower part of cylindrical wall 41 fonns a proper pressure cabin 46. The lower end of the moving contact 44 is jointed mechanically to the coupler 47 on the top of piston rod 33 through a suitable linkage. Thus, the motion of moving contact 44 is transmitted to the piston rod 33.

, Both FIG. 1 and FIG. 4 show the closed position of the breaker. Under the condition as indicated in FIG. 1, piston rod 33 and piston 32 are in the upper limit and is at rest and the external cylinder also is at rest against the spring by fitting of the top end of piston 32 and bridge end 26.

At first, opening operation without current and small current interrupting action are described as follows:

As the moving contact begins its parting motion, mechanically coupled piston rod 33 and consequently piston 32 desqend within the internal cylinder 17. In the quenching chamber without generation of gas pressure in case of no current opening, or with slight gas pressure in case of small current interruption, the parting speed of the moving contact and consequently the descending speed of the piston are slower than in case of large current interruption. By the action of spring 24, external cylinder 22 goes down at nearly the same speed as the piston speed. That is, the cylinder 22 goes down following the piston.

When piston 32 proceeds into the internal cylinder 17 the oil contained is compressed. But at the beginning of the piston motion, the oil flows out of the cylinder 22 through the clearances between bridge legs 28 of the cylinder 22 and slots 18 and 19 of the internal cylinder 17 and there is no braking action against the piston motion. When the piston 32 has passed the slots, the external cylinder which is going down following the piston comes to a position at which the two holes 30, 31 coincide with the two holes 20, 21 on the internal cylinder and the bottom of the cylinder 22 touches the base surface 12 of the body case 11 to stop further lowering. Under the condition, when the piston goes farther down, the oil in cylinder 17 flows out from the holes 20 and 30 or 21 and 31 so that damping action against the piston motion does not exist. When the piston 32 farther proceeds until its bottom surface goes beyond the position of hole 21, cylinder oil is compressed and a first weak damping action arises. But this action will rather help weaken the shock of clash against the projection l3.The moving contact 44 leaves the chamber before the bottom of cylinder touches the base projecting 13.

When interrupting large current, the actions are as follows:

When the moving contact 44 leaves the stationary contacts, gas pressure is generated by the are between both contacts and accelerates the lowering velocity of the moving contact. The piston 32 descends faster than the external cylinder does by aid of the spring 24. Until the piston has reached the lower edge of the slots 18, 19 the action is similar to the above mentioned for small current interruption. When the piston has passed the slots, the external cylinder has not lowered to such an extent that the holes 30 and 31 coincide with the holes 20 and 21 on the internal cylinder so that the oil in cylinder 17 is ocmpressed by piston 32, and braking action acts on the piston. The speed of the piston is decreased quickly. This means decrease of the moving contact speed. At this time, the moving contact is situated at the position most suitable for interruption.

In FIG. 4, when the above mentioned braking acts on the moving contact it is going down in the chamber near to the oiljet opening 45. At this position, the moving contact has sufficient parting distance from the stationary contact for recovery of the insulation, and by the gas pressure generated by are heat the oil at the top of the moving contact is disturbed and oil is blown out through the oil-jet openings mainly 45 or also 45,, 45,, from the chamber. Owing to this braking action, the moving contact takes comparatively long time to pass through the neighborhood of the most suitable position for interruption. Where the moving contact is existing within such position as mentioned above, there are chances to encounter zerocurrent at least once. Even if the interruption was unsuccess ful at the first zero-current, success is expected at the next or following zero-current time. Thus, the reliability to the interrupting capability is increased. Thereafter piston moves downward successively, and the external cylinder also goes down. When the two holes 30 and 31 coincide with the holes 20 and 21, the braking action is decreased, and the lowering speed of the piston isincreased. Accordingly, the moving contact motion becomes more rapid. The suitable position for interruption varies with the interrupting current, because the generated gas pressure varies with the current, accordingly the degree of accelerating the moving contact motion is changed. This is the reason why more than one oil-jet opening are provided along the route for the moving contact 44 as shown in FIG. 4, so as to be capable of interrupting all currents in an intended range.

FIG. 5 shows the characteristic curves with the braking device. The curves are indicated in time (X-axis) and transferring distance (Y-axis) 5,, means the starting time when the moving contact begins to part the stationary contacts and 8 5, means the distance from the stationary contact to final static position of the moving contact at the end of its whole movement. The characteristic for no current operation or small current interrupting is indicated by curve C,, and curve C, is for the case of large current interruption. S, is a position at which the braking action begins and corresponds to distance (from S to the upper internal surface a (FIG. 4 of jet opening 45 S is a position at which the braking action finishes, and corresponds to distance (from S,,) to the lower internal surface b (FIG. 4) of jet opening 45 From the drawing it is understood that curve C, is nearly a straight line, with a gentle slope for the final motion of the contact 44 receiving shock-absorbing action. Curve C indicates that the moving contact reaches S, in less time of t,, than in case of C, and takes longer time t,, to move up to 8,. If the suitable position for the interrupting currentis in neighborhood of opening 45,, moving velocity of the contact 44 is suddenly decreased. Therefore, when passing the position, the chance of encountering zero-current is surely increased. The distance to S, beginning the braking action becomes longer with the interrupting current increases and vice versa.

According to this invention, the following advantages are attained:

When the moving contact is passing the neighborhood of the most suitable position for are extinguishing, a kind of braking action is given to the motion of the contact, thereby lengthening the time duration required to pass the position, and the number of chances to encounter the zero-current in the position is increased. Thus, the interruption is surely achieved while moving contact is within the quenching chamber. Furthermore, any extension of the chamber is unnecessary to get the sure interruption.

, What we claim is:

1. An oil circuit breaker comprising: an arc-extinguishing chamber; stationary contacts arranged in said chamber; at least one movable contact adapted to depart, at the time of interruption, from said stationary contacts to travel through said chamber and to finally to go out thereof; and a braking device including means adapted to perform braking action on said movable contact when said contact passes the position moist suitable for are extinguishing, so as to make it easier for the zero-current time to be encountered, and further including means for releasing said braking action on said movable contact when it has passed the neighborhood of said most suitable position at the time of interruption. 

1. An oil circuit breaker comprising: an arc-extinguishing chamber; stationary contacts arranged in said chamber; at least one movable contact adapted to depart, at the time of interruption, from said stationary contacts to travel through said chamber and to finally to go out thereof; and a braking device including means adapted to perform braking action on said movable contact when said contact passes the position moist suitable for arc extinguishing, so as to make it easier for the zero-current time to be encountered, and further including means for releasing said braking action on said movable contact when it has passed the neighborhood of said most suitable position at the time of interruption. 